Oil pump rotor

ABSTRACT

Provided is an oil pump rotor capable of improving a volume efficiency and a quietness. When a diameter of a base circle bi of an inner rotor is Φ bi; a diameter of a first outer rolling circle Di is Φ Di; a diameter of a first inner rolling circle di is Φ di; a diameter of a base circle bo of an outer rotor is Φ bo; a diameter of a second outer rolling circle Do is Φ Do; a diameter of a second inner rolling circle do is Φ do; and an eccentricity amount between the inner rotor and the outer rotor is e, Φ bi=n·(Φ Di+Φ di) and Φ bo=(n+1)·(Φ Do+Φ do) hold; either Φ Di+Φ di=2e or Φ Do+Φ do=2e holds; and Φ Do&gt;Φ Di and Φ di&gt;Φ do hold. When a clearance between the inner rotor and the outer rotor is t, 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6 holds, provided that Φ Di+Φ di=2e; or 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6 holds, provided that Φ Do+Φ do=2e.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application is a U.S. National Phase Application under 35 U.S.C.§371 of International Patent Application No. PCT/JP2012/082423, filedDec. 13, 2012, and claims the benefit of Japanese Patent Application No.2011-273866, filed on Dec. 14, 2011, all of which are incorporated byreference in their entirety herein. The International Application waspublished in Japanese on Jun. 20, 2013 as International Publication No.WO/2013/089203 under PCT Article 21(2).

FIELD OF THE INVENTION

The present invention relates to an oil pump rotor capable of drawing inand then discharging a fluid as volumes of cells formed between an innerrotor and an outer rotor change.

BACKGROUND OF THE INVENTION

A conventional oil pump includes: an inner rotor having n (n is anatural number) external teeth; an outer rotor having n+1 internal teeththat are engageable with the external teeth; and a casing having anintake port for drawing in a fluid and a discharge port for dischargingthe same. Particularly, the external teeth and the internal teeth engagewith one another as the inner rotor rotates, thereby allowing the outerrotor to rotate such that a fluid can be drawn in and discharged asvolumes of a plurality of cells formed between the two rotors change.

The cells are individually established as the external teeth of theinner rotor and the internal teeth of the outer rotor individually comeinto contact with one another on a forward side and a backward side of arotational direction. Further, each cell has both of its side surfacessurrounded by the casing. Thus, the cells are configured as individualfluid transferring chambers. Particularly, each cell draws in a fluid asthe volume thereof enlarges when moving along the intake port, after thevolume of the corresponding cell has reached its minimum level duringthe process of engaging the external teeth and the internal teeth withone another. In contrast, the cell discharges the fluid as the volumethereof decreases when moving along the discharge port, after the volumeof the corresponding cell has reached its maximum level during theaforementioned process.

Since an oil pump configured as above is small and has a simplestructure, it can be widely used as, for example, a lubricating oil pumpand an automatic transmission oil pump that are installed inautomobiles. When used in an automobile, the oil pump is driven by, forexample, allowing the inner rotor to be directly coupled to a crankshaftof an engine such that the oil pump can be driven as the engine rotates;or the oil pump may also be driven by, for example, allowing the innerrotor to be coupled to an electric motor.

As for the aforementioned oil pump, for the purpose of reducing thenoise of the pump and improving a mechanical efficiency, tip clearancesof an appropriate size are provided between the tooth tips of the innerrotor and the tooth tips of the outer rotor at where the inner rotor andthe outer rotor, while being coupled to each other, have been rotated by180° from an engagement point.

Here, the conditions required for determining the tooth shapes of aninner rotor ri and an outer rotor ro are as follows. That is, as for theinner rotor ri, rolling distances of a first outer rolling circle Di′(diameter ΦDi′) and a first inner rolling circle di′ (diameter Φdi′)should add up to one cycle. That is, the rolling distances of the firstouter rolling circle Di′ and the first inner rolling circle di′ shouldaltogether be equal to the circumference of a base circle bi′ (diameterΦbi′) of the inner rotor ri, and henceΦ bi′=n·(Φ Di′+Φ di′)

Likewise, as for the outer rotor ro, rolling distances of a second outerrolling circle Do′ (diameter ΦDo′) and a second inner rolling circle do′(diameter Φdo′) should altogether be equal to the circumference of abase circle bo′ (diameter Φbo′) of the outer rotor ro, and hence.Φ bo′=(n+1)·(Φ Do′+Φ do′)Next, since the inner rotor ri and the outer rotor ro are to be engagedwith each other, the expression

-   Φ Di′+Φ di′=Φ Do′+Φ do′=2 e′ holds, provided that an eccentricity    amount of the two rotors ri and ro is e′. Based on the    aforementioned expressions, the expression-   n·Φ bo′=(n+1)·Φ bi′ holds. The tooth shapes of the inner rotor ri    and the outer rotor ro are configured to satisfy these requirements.    Here, by satisfying the expressions    Φ Do′=Di′+t/2, Φ do′=di′−t/2-   (t: clearance between the external teeth of the inner rotor ri and    the internal teeth of the outer rotor ro), not only a clearance t/2    (tip clearance tt) is formed at the tip section as shown in FIG. 14    and FIG. 15, but a clearance (side clearance ts) between the tooth    surfaces is also formed.

FIG. 13 to FIG. 15 show an oil pump rotor of an first example ofconventional arts that meets the aforementioned conditions. As for theinner rotor ri of this oil pump rotor, the base circle bi′ has adiameter of Φ bi′=44.80 mm; the first outer rolling circle Di′ has adiameter of Φ Di′=3.60 mm; the first inner rolling circle di′ has adiameter of Φ di′=2.80 mm; and the teeth number is n=7. As for the outerrotor ro, the outer diameter thereof is Φ 65 mm; the base circle bo′ hasa diameter of Φ bo′=51.20 mm; the second outer rolling circle Do′ has adiameter of Φ Do′=3.663 mm; the second inner rolling circle do′ has adiameter of Φ do′=2.737 mm; and the teeth number is (n+1)=8. Inaddition, the eccentricity amount is e′=3.2 mm.

As for the oil pump rotor of Japanese Patent No. 3734617 (referred to asfirst example of conventional arts hereunder) that has theaforementioned structure, the two rotors are so configured that thetooth shapes of the tooth tips of the inner rotor are formed smallerthan the tooth shapes of the tooth grooves of the outer rotor, and thatthe tooth shapes of the tooth grooves of the inner rotor are formedlarger than the tooth shapes of the tooth tips of the outer rotor. Forthis reason, a backlash and the tip clearance tt can respectively be setto be appropriately large, thereby making it possible to secure a largebacklash while maintaining a small tip clearance tt. Thus, in a statewhere an oil pressure supplied to the oil pump rotor and a torque fordriving the oil pump rotor are stable, it is possible to restrict theoccurrence of the noises resulting from the collision between theexternal teeth of the inner side and the internal teeth of the outerside.

However, by adjusting the diameters of the second outer rolling circleDo′ and the second inner rolling circle do′ of the outer rotor in thismanner, securing the tip clearance tt=t/2 shall inevitably cause theside clearance is to become large as shown in FIG. 14 and FIG. 15.Accordingly, the following problem remains unsolved with regard to thequietness of this oil pump rotor. That is, when the oil pressureoccurring in the oil pump rotor is minute and the torque for driving theoil pump rotor changes, the internal teeth of the outer side and theexternal teeth of the inner side collide with one another such thatcollision energies at that time are turned into sounds. Those sounds canthen be turned into noises after reaching an audible level.

An oil pump rotor configured in view of the aforementioned problem (e.g.Japanese Patent No. 4485770) has been proposed. As shown in FIG. 7 andFIG. 8, this oil pump rotor includes: an inner rotor 10 having “n” (n isa natural number) external teeth 11; an outer rotor 20 having “n+1”internal teeth 21 engageable with the external teeth 11; and a casing 50having an intake port for a fluid to be drawn thereinto and a dischargeport for the fluid to be discharged therefrom. Particularly, this oilpump rotor is used in an oil pump transferring a fluid by drawing in anddischarging the same as volumes of cells formed between the toothsurfaces of the two rotors 10, 20 change when the two engaged rotors 10,20 rotate. As for the aforementioned inner rotor 10, the shape of eachtooth tip is established by an epicycloid curve that is generated by afirst outer rolling circle Di externally tangent to and rolling on abase circle bi of the inner rotor 10 without slipping. The shape of eachtooth groove of the inner rotor 10 is established by a hypocycloid curvethat is generated by a first inner rolling circle di internally tangentto and rolling within the base circle bi without slipping. As for theaforementioned outer rotor 20, the shape of each tooth groove isestablished by an epicycloid curve that is generated by a second outerrolling circle Do externally tangent to and rolling on a base circle boof the outer rotor 20 without slipping. The shape of each tooth tip ofthe outer rotor 20 is established by a hypocycloid curve that isgenerated by a second inner rolling circle do internally tangent to androlling within the base circle bo without slipping. The inner rotor 10and the outer rotor 20 are so configured that when the diameter of thebase circle bi of the inner rotor 10 is Φ bi; the diameter of the firstouter rolling circle Di is Φ Di; the diameter of the first inner rollingcircle di is Φ di; the diameter of the base circle bo of the outer rotor20 is Φ bo; the diameter of the second outer rolling circle Do is Φ Do;the diameter of the second inner rolling circle do is Φ do; and aneccentricity amount between the inner rotor 10 and the outer rotor 20 ise, the expression Φ bi=n·(Φ Di+Φ di) and the expression Φ bo=(n+1)·(ΦDo+Φ do) hold; the expression Φ Di+Φ di=2 e or Φ Do+Φ do=2 e holds; andthe expressions Φ Do>Φ Di, Φ di>Φ do and (Φ Di+Φ di)<(Φ Do+Φ do) hold.Here, a backlash at an engagement point where a tooth tip of the outerrotor 20 and a tooth groove of the inner rotor 10 directly face eachother; and a backlash during the process where the volumes of the cellsincrease and decrease, are smaller than a backlash at where the volumeof a cell reaches its maximum level.

As for the oil pump rotor of Japanese Patent No. 4485770, the two rotors10 and 20 exhibit small backlashes such that an oil pump rotor superiorin quietness can be obtained. Particularly, the oil pressure occurringin the oil pump rotor is minute; and even if the torque for driving thisoil pump rotor changes, noise occurrence due to the collisions betweenthe internal teeth 21 of the outer side and the external teeth 11 of theinner side can be reliably restricted.

Problems to be Solved by the Invention

As for the oil pump of the Japanese Patent No. 4485770, the backlash atthe engagement point where the tooth tip of the outer rotor 20 and thetooth groove of the inner rotor 10 directly face each other; and thebacklash during the process where the volumes of the cells increase anddecrease, are smaller than the backlash at where the volume of a cell Creaches its maximum level. Since the backlash at the engagement pointwhere the tooth tip of the outer rotor 20 and the tooth groove of theinner rotor 10 directly face each other is small, even if the torque fordriving this oil pump rotor changes, noise occurrence due to thecollisions between the internal teeth 21 of the outer side and theexternal teeth 11 of the inner side can be reliably restricted. However,there arises a concern that vibration sounds may occur due to a rotationfluctuation caused by the acceleration or deceleration of the outerrotor 20.

FIG. 9 to FIG. 12 are diagrams showing correlations between angles ofrotation of the inner rotor 10 and intertooth clearances with regard tothe oil pump rotor of the second example of conventional arts. Here,intertooth clearances refer to clearances between the internal teeth 21of the outer rotor 20 and the external teeth 11 of the inner rotor 10,in a rotational direction of the corresponding external teeth. Shown inthese diagrams are correlations between the angles of rotation θ of theinner rotor 10 and the intertooth clearances at the locations of I, II,III and VI. An angle of rotation θ is the angle ranging over one toothof the inner rotor 10. The location of I is a location where a toothgroove of the outer rotor 20 and a tooth tip of the inner rotor 10engage with each other. As the engaged state at the location of Irotates by about ½ of the angle of rotation θ ranging over one tooth,the intertooth clearance at the location of I shall slightly increase,whereas the intertooth clearance at the location of VI shall rapidlydecrease, thus allowing the engaged state to switch from the location ofI to the location of VI at an engagement switching point. Here, it isunderstood that the intertooth clearances at the locations of II and IIIalso vary.

Next, diagrammatically shown in FIG. 10 by arrows YI and YVI are thedisplacement velocities of respectively the intertooth clearance at thelocation of I and the intertooth clearance at the location of VI, at the“engagement switching point.” Since the displacement velocities of thetwo are not synchronized, tooth contact noises occur as the engagementswitches.

Further, as shown in FIG. 11, in a range where the angle of rotation θof the inner rotor 10 reaches the “engagement switching point” from 0degree, since the intertooth clearance at the location of I remainssubstantially constant before reaching the “engagement switching point”by slightly increasing, a state of “minute deceleration” where therotary speed of the outer rotor 20 slightly decreases is observed on theleft side of the “engagement switching point” in the diagram. Incontrast, it is clear that beyond the “engagement switching point”toward the right side of the diagram, since the intertooth clearance atthe location of VI keeps decreasing until a slope of change thereofreaches 0, the rotation of the outer rotor 20 accelerates during suchperiod, and then allows the intertooth clearance to gradually increasethereafter such that the state of “minute deceleration” is established.In this way, since the outer rotor 20 switches from the state of minutedeceleration to the state of acceleration before and after the“engagement switching point,” there arises a concern that vibrationnoises may occur.

Further, when improving a fluid tightness by reducing a backlash atwhere the cell C reaches its maximum level for the purpose of improvingvolume efficiency, the backlashes between the teeth shall become smallas a whole, thus resulting in a situation in which since the backlashesat where the tooth tips of the inner rotor and the tooth grooves of theouter rotor engage by directly facing one another are exceedingly small,the teeth may interfere with one other due to a variation in the shapesthereof such that noises may occur.

SUMMARY OF THE INVENTION

Here, it is an object of the present invention to provide an oil pumprotor having an inner rotor and an outer rotor whose teeth are bothformed into appropriate shapes; and exhibiting a constant minimumintertooth clearance between the two rotors such that a quietness and avolume efficiency can be improved thereby.

Particularly, the minimum intertooth clearance refers to a clearance bywhich the external teeth 11 of the inner rotor and the internal teeth 21of the outer rotor are at their closest to each other regardless of arotational direction.

The invention of a first aspect is an oil pump rotor for use in an oilpump transferring a fluid by drawing in and discharging the fluid asvolumes of cells formed between tooth surfaces of two rotors change whenthe two rotors rotate while being engaged with each other, comprising:

an inner rotor having n (n is a natural number) external teeth, theinner rotor exhibiting a tooth tip shape established by an epicycloidcurve that is generated by a first outer rolling circle Di externallytangent to and rolling on a base circle bi of the inner rotor withoutslipping and a tooth groove shape established by a hypocycloid curvethat is generated by a first inner rolling circle di internally tangentto and rolling within the base circle bi without slipping;

an outer rotor having n+1 internal teeth, the outer rotor exhibiting atooth groove shape established by an epicycloid curve that is generatedby a second outer rolling circle Do externally tangent to and rolling ona base circle bo of the outer rotor without slipping and a tooth tipshape established by a hypocycloid curve that is generated by a secondinner rolling circle do internally tangent to and rolling within thebase circle bo without slipping; and a casing having an intake port fordrawing in a fluid and a discharge port for discharging the fluid,wherein

when a diameter of the base circle bi of the inner rotor is Φ bi; adiameter of the first outer rolling circle Di is Φ Di; a diameter of thefirst inner rolling circle di is Φ di; a diameter of the base circle boof the outer rotor is Φ bo; a diameter of the second outer rollingcircle Do is Φ Do; a diameter of a second inner rolling circle do is Φdo; and an eccentricity amount between the inner rotor and the outerrotor is e, Φ bi=n·(Φ Di+Φ di) and Φ bo=(n+1)·(Φ Do+Φ do) hold; either ΦDi+Φ di=2 e or Φ Do+Φ do=2 e holds; and Φ Do>Φ Di, Φ di>Φ do and (Φ Di+Φdi)<(Φ Do+Φ do) hold, and wherein

when a clearance between the inner rotor and the outer rotor is t,0.3<((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6 holds, provided that Φ Di+Φdi=2 e; or 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6 holds, provided that ΦDo+Φ do=2 e.

According to the invention of an second aspect, the external teeth ofthe inner rotor and the internal teeth of the outer rotor exhibittherebetween a minimum intertooth clearance with a deviation of notlarger than 10 at all locations where the external teeth of the innerrotor and the internal teeth of the outer rotor are adjacent to oneanother.

According to the invention of a third aspect, the deviation of theminimum intertooth clearance is not larger than 5 μm.

According to the invention of a fourth aspect, the minimum intertoothclearance is 35 to 45 μm.

According to the invention of a fifth aspect, the minimum intertoothclearance is 37.5 to 42.5 μm.

Effects of the Invention

According to the aforementioned structure, there can be obtained an oilpump rotor having a superior quietness. Particularly, since thedisplacement velocities of the intertooth clearances before and afterthe engagement switches are synchronized, and since the engagementintertooth clearances can be made substantially uniform, tooth contactnoises and noises due to a rotation fluctuation of the outer rotor canbe restricted. Further, for the purpose of improving volume efficiency,by reducing the minimum intertooth clearance at where the cell C reachesits maximum level, the teeth can be prevented from interfering with oneanother and noises can be restricted due to the fact that the minimumintertooth clearances at other locations shall not be small even whenimproving a fluid tightness.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome more readily appreciated when considered in connection with thefollowing detailed description and appended drawings, wherein likedesignations denote like elements in the various views, and wherein:

FIG. 1 is a plane view of an oil pump rotor of a first embodiment of thepresent invention.

FIG. 2 is an enlarged view of an engaged section of the oil pump rotorof the first embodiment shown in FIG. 2.

FIG. 3 is a plane view of the oil pump rotor of the first embodiment, inwhich locations of minimum intertooth clearances are shown.

FIG. 4 is a graph showing correlations between rotor revolution andsound pressure with regard to an oil pump of the present invention andan oil pump of the second example of conventional arts.

FIG. 5 is a graph comparing the minimum intertooth clearances of the oilpump rotor of the present invention and the oil pump rotors of the firstand second examples of conventional arts.

FIG. 6 is a graph showing a correlation between the minimum intertoothclearances and angles of rotation of an inner rotor.

FIG. 7 is a plane view of an oil pump rotor of the second example ofconventional arts.

FIG. 8 is an enlarged view of an engaged section of an oil pump of thesecond example of conventional arts shown in FIG. 7.

FIG. 9 is a graph showing a correlation between intertooth clearancesand angles of rotation of an inner rotor of the second example ofconventional arts.

FIG. 10 is a graph showing the correlation between intertooth clearancesand angles of rotation of the inner rotor of the second example ofconventional arts, in which the displacement velocities of theintertooth clearances are diagrammatically indicated by arrows.

FIG. 11 is a graph showing the correlation between intertooth clearancesand angles of rotation of the inner rotor of the second example ofconventional arts, in which diagrammatically indicated are ranges ofminute deceleration, acceleration and then minute deceleration of anouter rotor of the second example of conventional arts.

FIG. 12 is a graph showing the correlation between intertooth clearancesand angles of rotation of the inner rotor of the second example ofconventional arts, in which engagement intervals I and VI arediagrammatically indicated.

FIG. 13 is a plane view of an oil pump rotor of the first example ofconventional arts.

FIG. 14 is an enlarged view of an engaged section of an oil pump of thefirst example of conventional arts shown in FIG. 13.

FIG. 15 is an enlarged view of the engaged section of the oil pump ofthe first example of conventional arts, showing an engaged state of atooth tip of an outer rotor and a tooth groove of an inner rotor.

DETAILED DESCRIPTION OF THE INVENTION

Preferred embodiments of the present invention are described in detailwith reference to the accompanying drawings. However, the embodimentsshown hereunder shall not limit the contents of the present inventionthat are described in this application. Further, not all elementsdescribed hereunder are essential to the present invention. Since eachembodiment employs an unconventional oil pump rotor, an unconventionaloil pump rotor is obtained. This oil pump rotor is disclosed hereunder.

First Embodiment

A first embodiment of the present invention is described in detail withreference to the accompanying drawings. Here, elements identical tothose of examples of conventional arts are given identical symbols inthe following description. As shown in FIG. 1 to FIG. 3, an oil pumprotor includes: an inner rotor 10 having “n” external teeth (n is anatural number; n=7 in this embodiment); and an outer rotor 20 having“n+1” (8 in this embodiment) internal teeth engageable with the externalteeth. The inner rotor 10 and the outer rotor 20 are received in acasing 50.

Here, a plurality of cells C are formed between the tooth surfaces ofthe inner rotor 10 and the outer rotor 20 in a manner such that thecells C are actually provided along rotational directions of the rotors10, 20. In a forward and backward rotational directions of the rotors10, 20, each cell C is individually established as a result of allowingexternal teeth 11 of the outer rotor 10 and internal teeth 21 of theouter rotor 20 to come into contact with one another; and both sides ofthis cell C are surrounded by the casing 50. In this way, there areformed individual fluid transfer chambers. Moreover, the cells C rotateas the rotors 10, 20 rotate, in a manner such that each cell Crepeatedly exhibits an increase and decrease in its volume within eachrotational cycle as one cycle.

The inner rotor 10 is attached to a rotary shaft, and is rotatablysupported thereby around a shaft center Oi. The shape of each tooth tipof the inner rotor 10 is established by an epicycloid curve that isgenerated by a first outer rolling circle Di externally tangent to androlling on a base circle bi of the inner rotor 10 without slipping. Theshape of each tooth groove of the inner rotor 10 is established by ahypocycloid curve that is generated by a first inner rolling circle diinternally tangent to and rolling within the base circle bi withoutslipping.

The outer rotor 20 whose shaft center is Oo is eccentrically disposedwith respect to the shaft center Oi of the inner rotor 10 (eccentricityamount: e), and is rotatably supported within the casing 50 about theshaft center Oo. The shape of each tooth groove of the outer rotor 20 isestablished by an epicycloid curve that is generated by a second outerrolling circle Do externally tangent to and rolling on a base circle boof the outer rotor 20 without slipping. The shape of each tooth tip ofthe outer rotor 20 is established by a hypocycloid curve that isgenerated by a second inner rolling circle do internally tangent to androlling within the base circle bo without slipping.

The following relational expressions hold between the inner rotor 10 andthe outer rotor 20, provided that a diameter of the base circle bi ofthe inner rotor 10 is Φ bi; a diameter of the first outer rolling circleDi is Φ Di; a diameter of the first inner rolling circle di is Φ di; adiameter of the base circle bo of the outer rotor 20 is Φ bo; a diameterof the second outer rolling circle Do is Φ Do; and a diameter of thesecond inner rolling circle do is Φ do. Here, mm (millimeter) is used asthe measurement unit.

As for the inner rotor 10, rolling distances of the first outer rollingcircle Di and the first inner rolling circle di should add up to onecycle. That is, the rolling distances of the first outer rolling circleDi and the first inner rolling circle di should altogether be equal tothe circumference of the base circle bi.Φ bi=n·(Φ Di+Φ di)   (Ia)Likewise, as for the outer rotor 20, rolling distances of the secondouter rolling circle Do and the second inner rolling circle do shouldaltogether be equal to the circumference of the base circle bo.Φ bo=(n+1)·(Φ Do+Φ do)   (Ib)

Further, as for the shapes of the tooth tips of the inner rotor 10 thatare established by the first outer rolling circle Di and correspond tothe shapes of the tooth grooves of the outer rotor 20 which areestablished by the second outer rolling circle Do; and as for the shapesof the tooth tips of the outer rotor 20 that are established by thesecond inner rolling circle do and correspond to the shapes of the toothgrooves of the inner rotor 10 which are established by the first innerrolling circle di, the following relational expressions have to holdsuch that backlashes between the tooth surfaces of the two rotors 10 and20 can be secured in a large magnitude during an engagement process.Φ Do>Φ Di, and Φ di>Φ do

Here, the backlashes refer to clearances that are formed, during theengagement process, between the tooth surfaces of the outer rotor 20 andthe tooth surfaces of the inner rotor 10, the tooth surfaces of theinner rotor 10 in such case being the tooth surfaces opposite to thosesubjected to loads.

Further, in order for the inner rotor and the outer rotor to engage witheach other, either one of Φ Di+Φ di=2 e and Φ Do+Φ do=2 e has to hold.

In the present invention, in order for the inner rotor 10 tosuccessfully rotate inside the outer rotor 20; the magnitude of thebacklashes to be optimized, and an engagement resistance to be reduced,while securing tip clearances, the diameter of the base circle bo of theouter rotor 20 is formed large such that the base circle bi of the innerrotor 10 and the base circle bo of the outer rotor 20 will not come intocontact with each other at an engagement point of the inner rotor 10 andthe outer rotor 20. That is, a relational expression (n+1)·Φ bi<n·Φ boholds.

Obtained from this expression, expressions (Ia) and (Ib) is(Φ Di+Φ di)<(Φ Do+Φ do).

Particularly, the aforementioned engagement point refers to a pointwhere, as shown in FIG. 2, a tooth groove of an internal tooth 21 of theouter side directly faces a tooth tip of an external tooth 11 of theinner side.

Moreover, the inner rotor 10 and the outer rotor 20 are so configuredthat when a clearance between the inner rotor and the outer rotor is“t”,0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6   (Ic),provided that Φ Di+Φ di=2e; or0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6   (Ic),provided that Φ Do+Φ do=2e holds

((Φ Do+Φ do)−(Φ Di+Φ di)) is referred to, hereunder, as a difference intooth depth between the internal tooth 21 of the outer rotor 20 and theexternal tooth 11 of the inner rotor 10). Particularly, in (expressionIc), the unit of “clearance t” is mm (millimeter). Further, the toothdepth refers to the dimension of each tooth in the normal direction.

Further, a minimum intertooth clearance ts between the internal tooth 21of the outer rotor 20 and the external tooth 11 of the inner rotor 10 atthe engagement point shown in FIG. 2 (the lowermost part in FIG. 1)where the tooth groove and the tooth tip directly face each other,serves as a side clearance formed on both sides of the internal tooth 21and external tooth 11 in the rotational directions thereof. Here, sincethe internal tooth 21 also has an intertooth clearance formed in adirection opposite to the rotational direction thereof, the smallerclearance is referred to as the minimum intertooth clearance in thedescription of the present embodiment.

FIG. 3 shows the locations of the minimum intertooth clearances ts. Whenrotationally driving the inner rotor 10 in the counterclockwisedirection, a minimum intertooth clearance ts is formed on the rotationaldirection side of the external tooth 11 and a counter-rotationaldirection side of the internal tooth 21 at the location where the volumeof the cell C increases (the right side in FIG. 3); a minimum intertoothclearance ts is formed on the counter-rotational direction side of theexternal tooth 11 and the rotational direction side of the internaltooth 21 at the location where the volume of the cell C decreases (theleft side in FIG. 3); and a minimum intertooth clearance ts is formedbetween the tip of the external tooth 11 and the tip of the internaltooth 21 at a nonengagement point where the tooth tips directly faceeach other (the uppermost part in FIG. 1), the minimum intertoothclearance ts being substantially ½ the size of the clearance t.

Further, since the aforementioned (expression Ic) holds, as shown inFIG. 3, at all locations where the external teeth 11 of the inner rotor10 and the internal teeth 21 of the outer rotor 20 are adjacent to oneanother (e.g. the engagement points where the tooth grooves and thetooth tips directly face each other, the locations where the volumes ofthe cells C increase and decrease and the locations where the tooth tipsdirectly face each other), the minimum intertooth clearances ts betweenthe external teeth 11 of the inner rotor 10 and the internal teeth 21 ofthe outer rotor 20 can be formed substantially identical to one another.In the present embodiment, the minimum intertooth clearances ts in alllocations are set to be 40 μm, whereas a deviation of the minimumintertooth clearance ts to the value thus set is 10 μm, preferably in arange of not larger than 5 μm. The deviations of the minimum intertoothclearances ts of all locations to the set minimum intertooth clearancets are each within the range of not larger than 5 μm.

However, in the present embodiment, the inner rotor 10 (base circle bi,Φ bi=44.8 mm; first outer rolling circle Di, Φ Di=3.60 mm; first innerrolling circle di, Φ di=2.80 mm; teeth number n=7) and the outer rotor20 (outer diameter Φ 65.0 mm; base circle bo, Φ bo=51.24 mm; secondouter rolling circle Do, Φ Do=3.625 mm; second inner rolling circle do,Φ do=2.78 mm) are combined at an eccentricity amount of e=3.20 mm so asto compose the oil pump rotor. Further, in the present embodiment, atooth width (dimension in a rotary shaft direction) of both the rotorsis set to be 13.2 mm. Thus, a difference in tooth depth is 0.005 mm.Furthermore, the clearance t is t=0.08 mm (80 μm); the minimumintertooth clearance ts is ts=0.037 to 0.041 mm (37 to 41 μm); and avalue obtained with the expression (Ic) is 0.5. In this way, the minimumintertooth clearance ts is substantially ½ of the clearance t, and thedeviation is not larger than 5 μm.

As for the casing 50, among the cells C that are formed between thetooth surfaces of both the rotors 10 and 20, formed along a cell C whosevolume is in the process of increasing is an arc-shaped intake port (notshown), whereas formed along a cell C whose volume is in the process ofdecreasing is an arc-shaped discharge port (not shown).

The cells C are so configured that after the volume of a cell C hasreached its minimum level during the process of engaging an externaltooth 11 with an internal tooth 21, this cell C shall suck in a fluid byenlarging its volume when moving along the intake port; and that afterthe volume of this cell C has reached its maximum level, thecorresponding cell C shall then discharge the fluid by decreasing itsvolume when moving along the discharge port.

The aforementioned expression (Ic) involves a value obtained bymultiplying the difference in tooth depth by the teeth number n of theinner rotor 10 or by the teeth number (n+1) of the outer rotor 20; andthen diving by the clearance t. The expression (Ic) defines a range inwhich not only the minimum intertooth clearances ts of all locations canbe set to be small; but the deviations of the minimum intertoothclearances ts can also be small. When the teeth number n is large, it isnecessary to reduce the difference in tooth depth. In contrast, when theteeth number n is small, it is then necessary to make the difference intooth depth large. That is, the difference in tooth depth that changesas the teeth number n increases or decreases and the clearance t bear aproportionate relationship to each other within a given range.

In this way, since 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6 when Φ Di+Φdi=2 e, or since 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6 when Φ Do+Φ do=2e, the minimum intertooth clearances ts can be equalized and shrunk suchthat engagement noises or the like may be reduced and a volumeefficiency may be improved. If not exceeding 0.3 or if exceeding 0.6, itbecomes difficult to equalize the minimum intertooth clearances ts.

FIG. 5 shows a graph comparing: the intertooth clearance at each angleof rotation of an inner rotor used in an oil pump rotor of aconventional technique 1 (Japanese Patent No. 3734617) (dashed line inFIG. 5); the intertooth clearance at each angle of rotation of an innerrotor used in an oil pump rotor of a conventional technique 2 (JapanesePatent No. 4485770) (dashed-dotted line in FIG. 5); and the intertoothclearance at each angle of rotation of the inner rotor used in the oilpump rotor of the present embodiment (continuous line in FIG. 5).According to this graph, the oil pump rotor of the present embodimentwhich is the “invention” makes it possible for the minimum intertoothclearances of all locations to be formed small and substantiallyequalized. Therefore, while the conventional techniques bore a problemwhere a variation in tooth shape could have led to tooth interferencesin regions with small intertooth clearances, the developed product iscapable of securing appropriate intertooth clearances, thereby making itpossible to easily avoid the aforementioned problem and realize a smoothrotation. Here, in FIG. 5, the reason that only the intertoothclearances at the angles of rotation of 0° to 180° are denoted isbecause changes in intertooth clearance from 180° to 360° (0°) aresimilar to that from 180° to 0° shown in FIG. 5, thus omitting thedescription thereof.

Further, FIG. 6 shows a graph obtained by applying the graphs of FIG. 9to FIG. 12 of the examples of conventional arts to the “invention.” Asindicated by the symbols YI, YVI in FIG. 6, since the displacementvelocities are synchronized, engagement at the location of VI can startto take place smoothly, thus making it possible to restrict toothcontact noises. Moreover, a difference in intertooth clearance betweenthe locations of I and VI at/beyond an “engagement switching point” issmall (deviation of not larger than 5 μm, 1 to 3 μm in FIG. 6), thusmaking it possible to improve a contact ratio and restrict engagementmechanical noises. In addition, since the outer rotor 20 does notaccelerate or decelerate, rotational noises of the outer rotor 20 can berestricted, thereby improving quietness as a whole.

Here, shown in FIG. 4 are correlations between rotor revolution andsound pressure with regard to the oil pump of the present invention andthe conventional oil pump, from which it is understood that the presentinvention is capable of improving quietness.

Further, the minimum intertooth clearances is between the external teeth11 of the inner rotor 10 and the internal teeth 21 of the outer rotor 2are substantially equalized at all locations where the external teeth 11of the inner rotor 10 and the internal teeth 21 of the outer rotor 20are adjacent to one another (engagement points where the tooth groovesand tooth tips directly face one another; locations where the volumes ofthe cells C increase and decrease; and locations where the tooth tipsdirectly face one another). Therefore, for the purpose of improvingvolume efficiency, since the minimum intertooth clearances at thelocations where the cells C reach their maximum levels are reduced, theminimum intertooth clearance at each tooth shall not be exceedinglysmall even when attempting to improve fluid tightness. For this reason,appropriate intertooth clearances can be secured, thus making itpossible to prevent the teeth from interfering with one another andrestrict noises.

In this way, the oil pump rotor of the present embodiment describedabove includes: the inner rotor having “n” (n is a natural number)external teeth; the outer rotor having “n+1” internal teeth engageablewith the external teeth; and the casing having the intake port for afluid to be drawn thereinto and the discharge port for the fluid to bedischarged therefrom. Particularly, this oil pump rotor is used in anoil pump transferring a fluid by drawing in and discharging the same asthe volumes of the cells formed between the tooth surfaces of the tworotors change when the two engaged rotors rotate.

As for the aforementioned inner rotor, the shape of each tooth tip ofthe inner rotor is established by the epicycloid curve that is generatedby the first outer rolling circle Di externally tangent to and rollingon the base circle bi of the inner rotor without slipping. The shape ofeach tooth groove of the inner rotor is established by the hypocycloidcurve that is generated by the first inner rolling circle di internallytangent to and rolling within the base circle bi without slipping.

As for the aforementioned outer rotor, the shape of each tooth groove ofthe outer rotor is established by the epicycloid curve that is generatedby the second outer rolling circle Do externally tangent to and rollingon the base circle bo of the outer rotor without slipping. The shape ofeach tooth tip of the outer rotor is established by the hypocycloidcurve that is generated by the second inner rolling circle do internallytangent to and rolling within the base circle bo without slipping.

When the diameter of the base circle bi of the inner rotor is Φ bi; thediameter of the first outer rolling circle Di is Φ Di; the diameter ofthe first inner rolling circle di is Φ di; the diameter of the basecircle bo of the outer rotor is Φ bo; the diameter of the second outerrolling circle Do is Φ Do; the diameter of the second inner rollingcircle do is Φ do; and the eccentricity amount between the inner rotorand the outer rotor is e, the expression Φ bi=n·(Φ Di+Φ di) and theexpression Φ bo=(n+1)·(Φ Do+Φ do) hold; the expression Φ Di+Φ di=2 e orΦ Do+Φ do=2 e holds;

and the expressions Φ Do>Φ Di, Φ di>Φ do and (Φ Di+Φ di)<(Φ Do+Φ do)hold.

Here, the inner rotor and the outer rotor are also configured in amanner such that when Φ Di+Φ di=2 e, the expression 0.3≦((Φ Do+Φ do)−(ΦDi+Φ di))·(n+1)/t≦0.6 holds, or that

-   -   when Φ Do+Φ do=2 e, the expression 0.3≦((Φ Do+Φ do)−(Φ Di+Φ        di))·n/t≦0.6 holds, provided that the clearance between the        inner rotor and the outer rotor is t.

For this reason, there can be obtained an oil pump with a superiorquietness. Especially, since the minimum intertooth clearances ts can beequalized, contact noises, vibration sounds and engagement mechanicalnoises at the engagement switching point can be prevented from occurringsuch that not only the quietness of the oil pump rotor can be reliablyachieved, but the volume efficiency can be improved as a result ofimproving the sealability. Particularly, the deviation of the minimumintertooth clearance ts is set to be 10 μm, preferably in the range ofnot larger than 5 μm.

Further, as an effect of the embodiment, since the deviation of eachintertooth clearance ts to the inner rotor is constantly 10 μm,preferably not larger than 5 μm, under the condition in which when ΦDi+Φ di=2 e, the expression 0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6holds; or the condition in which when Φ Do+Φ do=2 e, the expression0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6 holds, the minimum intertoothclearances ts which are the appropriate clearance gaps can be secured atengaged sections even when the clearance t is formed small. Therefore,it is possible to avoid the interferences between the external teeth 11and the internal teeth 12 by absorbing variation in part accuracy,thereby realizing a smooth rotation, thus improving mechanicalefficiency. Moreover, by making the minimum intertooth clearances tssmall, e.g., as small as 35 to 45 μm, preferably 37.5 to 42.5 μm, thesealability between the external teeth 11 and the internal teeth 21 atwhere the volumes of the cells reach their maximum levels increases,thereby making it possible to improve volume efficiency.

However, the present invention is not limited to the aforementionedembodiment. In fact, various modified embodiments are possible.

DESCRIPTION OF THE SYMBOLS

10 inner rotor

11 external teeth

20 outer rotor

21 internal teeth

50 casing

Di outer rolling circle of inner rotor (first outer rolling circle)

Do outer rolling circle of outer rotor (second outer rolling circle)

di inner rolling circle of inner rotor (first inner rolling circle)

do inner rolling circle of outer rotor (second inner rolling circle)

C cell

bi base circle of inner rotor

bo base circle of outer rotor

Oi shaft center of inner rotor

Oo shaft center of outer rotor

t clearance

ts minimum intertooth clearance

The invention claimed is:
 1. An oil pump rotor for use in an oil pumptransferring a fluid by drawing in and discharging said fluid as volumesof cells formed between tooth surfaces of two rotors that change whensaid two rotors rotate while being engaged with each other, said oilpump rotor comprising: an inner rotor having n (n is a natural number)external teeth, said inner rotor exhibiting a tooth tip shapeestablished by an epicycloid curve that is generated by a first outerrolling circle Di externally tangent to and rolling on a base circle biof said inner rotor without slipping and a tooth groove shapeestablished by a hypocycloid curve that is generated by a first innerrolling circle di internally tangent to and rolling within said basecircle bi without slipping; an outer rotor having n+1 internal teeth,said outer rotor exhibiting a tooth groove shape established by anepicycloid curve that is generated by a second outer rolling circle Doexternally tangent to and rolling on a base circle bo of said outerrotor without slipping and a tooth tip shape established by ahypocycloid curve that is generated by a second inner rolling circle dointernally tangent to and rolling within said base circle bo withoutslipping; and a casing having an intake port for drawing in a fluid anda discharge port for discharging the fluid, wherein the inner and outerrotors are formed to satisfy:Φ bi=n(Φ Di+Φ di), Φ bo=(n+1)·(Φ Do+Φ do);Φ Di+Φ di=2e;Φ Do>Φ Di, Φ di>Φ do, (Φ Di+Φ di)<(Φ Do+Φ do),and,0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·(n+1)/t≦0.6;or,Φ bi=n·(Φ Di+Φ di), Φ bo=(n+1)·Φ Do+Φ do)Φ Do+Φ do=2eΦ Do>Φ Di, Φ di>Φ do, (Φ Di+Φ di)<(Φ Do+Φ do)and,0.3≦((Φ Do+Φ do)−(Φ Di+Φ di))·n/t≦0.6 where Φ bi, Φ Di, Φ di, Φ bo, ΦDo, Φ do, e, and t respectively indicate a diameter of said base circlebi, a diameter of said first outer rolling circle Di, a diameter of saidfirst inner rolling circle di, a diameter of said base circle bo, adiameter of said second outer rolling circle Do, a diameter of a secondinner rolling circle do, an eccentricity amount between said inner rotorand a said outer rotor and a clearance between said inner rotor and saidouter rotor.
 2. The oil pump rotor according to claim 1, wherein saidexternal teeth of said inner rotor and said internal teeth of said outerrotor exhibit there between a minimum inter-tooth clearance with adeviation of not larger than 10 μm, at all locations where said externalteeth of said inner rotor and said internal teeth of said outer rotorare adjacent to one another.
 3. The oil pump rotor according to claim 2,wherein said minimum inter-tooth clearance is 35 to 45 μm.
 4. The oilpump rotor according to claim 1, wherein said deviation of said minimuminter-tooth clearance is not larger than 5 μm.
 5. The oil pump rotoraccording to claim 4, wherein said minimum inter-tooth clearance is 37.5to 42.5 μm.